title: Pth1/Vam3p is the syntaxin homolog at the vacuolar membrane of Saccharomyces cerevisiae required for the delivery of vacuolar hydrolases.
abstract: The PEP12 homolog Pth1p (Pep twelve homolog 1) is predicted to be similar in size to Pep12p, the endosomal syntaxin homolog that mediates docking of Golgi-derived transport vesicles and, like other members of the syntaxin family, is predicted to be a cytoplasmically oriented, integral membrane protein with a C-terminal transmembrane domain. Kinetic analyses indicate that deltapth1/vam3 mutants fail to process the soluble vacuolar hydrolase precursors and that PrA, PrB and most of CpY accumulate within the cell in their Golgi-modified P2 precursor forms. This is in contrast to a pep12 mutant in which P2CpY is secreted from the cell. Furthermore, pep12 is epistatic to pth1/vam3 with respect to the CpY secretion phenotype. Alkaline phosphatase, a vacuolar membrane hydrolase, accumulates in its precursor form in the deltapth1/vam3 mutant. Maturation of pro-aminopeptidase I, a hydrolase precursor delivered directly to the vacuole from the cytoplasm, is also blocked in the deltapth1/vam3 mutant. Subcellular fractionation localizes Pth1/Vam3p to vacuolar membranes. Based on these data, we propose that Pth1/Vam3p is the vacuolar syntaxin/t-SNARE homolog that participates in docking of transport vesicles at the vacuolar membrane and that the function of Pth1/Vam3p impinges on at least three routes of protein delivery to the yeast vacuole.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA. amits@cmu.edu
authors.forename: A
authors.initials: A
authors.lastname: Srivastava
authors.forename: E W
authors.initials: EW
authors.lastname: Jones
mesh_terms: D000595:Amino Acid Sequence; D005452:Fluoresceins; D005456:Fluorescent Dyes; D005656:Fungal Proteins / Q000378:metabolism* / Q000502:physiology*; D017353:Gene Deletion; D005800:Genes, Fungal / Q000235:genetics; D006867:Hydrolases / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010641:Phenotype; D050765:Qa-SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions; D014617:Vacuoles / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D005656:Fungal Proteins; D008565:Membrane Proteins; C081224:PEP12 protein, S cerevisiae; D050765:Qa-SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C107706:VAM3 protein, S cerevisiae; C093616:6-carboxyfluorescein diacetate; D006867:Hydrolases